Use 'elvis' as example username instead of 'stefanl'

Long live the king; Stefan has left the building.

Submitters and reviewers please make sure

• internal links are relative and to the .md file
• avoid links named "here"
• alt-text for images is descriptive
• doesn't duplicate existing content
• spell check
• renders correctly
• does not include any identifiable information (real usernames, project names, etc)